1. Field of the Invention
The present invention relates to a magnetron plasma processing apparatus and a method of processing magnetron plasma available for the production of semiconductor integrated circuits.
2. Description of the Related Art
Conventional magnetron plasma etching or dry etching apparata generate an electric field between parallel plane electrodes and a magnetic field orthogonally intersecting the electric field. Such a conventional magnetron plasma etching apparatus executes an etching process against a semiconductor refer by generating plasma with etching gas to process this wafer mounted on one of those plane electrodes.
Normally, in order to promote anisotropy as the typical etching characteristic, such a conventional magnetron plasma etching apparatus cited above executes an etching process by maintaining the internal pressure of vacuum chamber very low like 3.5 m Torr, or 7 m Torr, or 9 m Torr, for example.
Although anisotropy is securely promoted in the course of etching the semiconductor wafer by holding the internal pressure of the vacuum chamber very low as cited above, the etching rate can hardly be maintained at a constant level on the semiconductor wafer. Inventors of the present invention detected that application of such low internal pressure to the etching process of a semiconductor wafer resulted in the generation of a faulty wafer shape, in the form of a bent or gouged configuration. After exploration of the cause of these faulty symptoms, the inventors confirmed that, when such low pressure was applied, due to least probability of generating collision between ions, the plasma remained in low density, and thus resulted in the generation of a comparatively thick plasma sheath (in other words, a dark sphere of plasma) in the neighborhood of the semiconductor wafer.
Based on this discovery, the inventors further detected that, after being released from the semiconductor wafer as a result of generating collision between electrons, secondary electrons performed cyclonic movement according to the relationship between the electric field and magnetic field, and then, even when the secondary electrons were supposed to traverse the plasma, the secondary electrons shifted themselves to one side without hitting against gas seeds, but instead, the secondary electrons moved themselves into the comparatively thick plasma sheath without traversing the plasma at all, and finally, accumulated on the peripheral edges of the semiconductor wafer.
Taking these symptoms into account, the inventors finally confirmed that the plasma could not maintain uniform density in the neighborhood of the semiconductor wafer, and yet, accumulated electrons adversely affected the etching characteristic.
Such a conventional magnetron plasma etching system has another technical problem to solve. Concretely, due to uneven intensity and direction of magnetic field, the etching process cannot properly be executed at minimum etching speed, and in addition, ions cannot hold own their directivity constant, but these ions are obliged to obliquely enter into the wafer substrate, thus eventually making it difficult to properly execute the etching process with satisfactory anisotropy.
Although not strictly being defined, a variety of physical reasons are assumed to adversely affect the etching process to result in the poor formation of the semiconductor wafer. More particularly, the line of magnetic force formed in the peripheral edges of the semiconductor wafer cannot be formed in parallel with the upper surface of the semiconductor wafer, but instead, it turns into a loop. Since the electric field remains comparatively less in the plasma, electrons are subject to intense influence of magnetic field, and as a result, electrons respectively perform spiral movement with a circle of about 2 mm across by way of surrounding the line of magnetic force. As a result, when the line of magnetic force intersects the semiconductor wafer, electrons obliquely enter into the wafer along the line of magnetic force.
On the other hand, those ions directly being applied to the etching process respectively contain substantial mass, and thus, these ions are rarely subject to deviation of their moving direction otherwise caused by direct influence of magnetic field. Nevertheless, when electrons obliquely enter into the semiconductor wafer substrate during the process, these electrons merely collide with one-side wall of the substrate to result in the uneven accumulation of charge on both-side walls, which in turn generates uneven and asymmetrically distributed charge. In consequence, a new electric field is generated on both sides of the semiconductor wafer substrate, which then affects ions so that ions are obliged to move in deviant directions. This eventually results in degraded anisotropy in the formation of semiconductor wafers.
To solve this problem, if a plurality of permanent magnets were provided on both ends of parallel plane electrodes consisting of substrate electrodes and opposite electrodes, the upper surface of the semiconductor wafer will be provided with a specific magnetic field which is approximately parallel. In this case, the conventional magnetron plasma processing apparatus can generate such a semiconductor wafer having satisfactory anisotropy. On the other hand, when disposing a plurality of permanent magnets on both sides of parallel plane electrodes, because of the positionwise relationship, it is extremely difficult for the system to rotate those permanent magnets. Furthermore, no art can materialize uniform etching effect without rotating those permanent magnets. Furthermore, in order to generate uniform magnetic field on the semiconductor wafer based on the structure cited above, the system needs to provide large size permanent magnets.
There is such a proposed conventional apparatus which disposes coil-like electrodes in the periphery of the vacuum chamber in place of those permanent magnets mentioned above. The proposed apparatus is characteristically capable of rotating the direction of magnetic field by feeding alternate current having phases 90.degree. apart from each other to the two pairs of coils orthogonally intersecting each other.
On the other hand, in order to uniformly feed magnetic field to the whole surface of the semiconductor wafer, these coils must respectively have substantial diameter in proportion to the dimension of the vacuum chamber. In other words, the greater the dimension of the semiconductive wafer, the greater the dimension needed for the coils. This in turn requires the power supply source to increase the power supply capacity. Furthermore, since the magnetic field intensely affects both the interior and exterior of the chamber including a possibly unwanted domain, the proposed magnetron plasma processing system cannot practically use such electronic elements which are extremely sensitive to magnetism, and yet, the proposed system needs to have an effective means to prevent magnetism from leaking out of the apparatus